Sumo is a much shorter bar path - especially if you can get wide naturally - with your toes out. Add in flats, and you can realistically remove 5-9 inches from your bar path. Complainers will complain, but its so useless - the sport is the sport - the rules are the rules.
Secondarily - sumo works a similar but different set of musculature - that often can help you break through a sticking point in your conventional.
End of the day - train both - the help each other. If you want to compete - consider sumo if you are flexible. If you are more comfortable in conventional - compete in that. Many many of the best deadlifters in the world are good at both, which is a useful data point.